Control device for internal combustion engine

ABSTRACT

A control device for an internal combustion engine includes a controller. The controller controls the relative rotation phase of the exhaust camshaft in accordance with the relative rotation phase of the intake camshaft. When a request for locking the relative rotation phase of the intake camshaft at an intermediate phase is generated, the controller controls the relative rotation phase of the exhaust camshaft such that the relative rotation phase of the exhaust camshaft is changed to a phase corresponding to the intermediate phase independently from the relative rotation phase of the intake camshaft.

TECHNICAL FIELD

The present invention relates to a control device for an internalcombustion engine capable of changing the valve timing of the intakevalves and the valve timing of the exhaust valves by changing therotation phase of the intake camshaft relative to the crankshaft.

BACKGROUND ART

Conventionally, an internal combustion engine including an intake-sidehydraulic drive variable valve timing mechanism is known. See, forexample, Patent Document 1. Such an engine changes the valve timing ofthe intake valves by changing the rotation phase of the intake camshaftrelative to the crankshaft with a variable valve timing mechanism.

The engine also includes a lock mechanism for mechanically locking therelative rotation phase of the intake camshaft at an intermediate phase,which is between the most retarded phase and the most advanced phase.Specifically, a vane rotor having vanes is arranged integrally with theintake camshaft. One of the vanes has a lock pin, which is selectivelyprojected and retracted by hydraulic pressure. The vane rotor isaccommodated in a housing, which rotates integrally with the crankshaftvia the timing chain. The housing has a lock hole, into which the lockpin can be inserted, and a ratchet groove, which extends from the lockhole to the phase retarding side and is shallower than the lock hole.

When a request for locking the relative rotation phase of the intakecamshaft at the intermediate phase at stoppage of the engine, thecontrol device for the engine controls the relative rotation phase ofthe intake camshaft such that the relative rotation phase of the intakecamshaft is changed to fall within a predetermined phase rangecorresponding to the ratchet groove and inserts the lock pin into theratchet groove. Then, when the intake camshaft is relatively rotated tothe intermediate phase through ratchet action, or, in other words, thelock pin is moved to the position of the lock hole through the relativerotation, the lock pin is inserted into the lock hole, thus bringingabout a locked state. In this manner, the relative rotation phase of theintake camshaft is mechanically locked at the intermediate phase. Therelative rotation phase of the intake camshaft is thus maintained at theintermediate phase, which is suitable for engine start, until the engineis re-started.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: Japanese Laid-Open Patent Publication No.    2011-32904

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

Some internal combustion engines have an exhaust-side hydraulic drivevariable valve timing mechanism, which, like the intake-side variablevalve timing mechanism, changes the valve timing of the exhaust valvesby changing the rotation phase of the exhaust camshaft relative to thecrankshaft. In some of these cases, to ensure cost-effectiveness, a lockmechanism is arranged only on the intake side and the exhaust-sidevariable valve timing mechanism is not provided with a lock mechanism.

If this is the case, the problem described below may occur when therelative rotation phase of the intake camshaft is locked at theintermediate phase. That is, the relative rotation phase of the exhaustcamshaft is set in accordance with the relative rotation phase of theintake camshaft such that the amount of valve overlap of the intakevalve and the exhaust valve becomes suitable for the current engineoperating state. Accordingly, as the intake camshaft is relativelyrotated toward the intermediate phase, the exhaust camshaft may berelatively rotated abruptly toward the phase corresponding to theintermediate phase in a manner following the relative rotation of theintake camshaft. In this case, although the relative rotation phase ofthe intake camshaft is locked at the intermediate phase, the relativerotation phase of the exhaust camshaft may overshoot the phase set inaccordance with the intermediate phase. This may cause an abrupt changein the engine output when the relative rotation phase of the intakecamshaft is locked at the intermediate phase.

Accordingly, it is an objective of the present invention to provide acontrol device for an internal combustion engine capable of restrainingan abrupt change of the engine output in a favorable manner when therotation phase of the intake camshaft relative to the crankshaft islocked at the intermediate phase.

Means for Solving the Problems

To achieve the foregoing objective and in accordance with one aspect ofthe present invention, a control device for an internal combustionengine is provided. The engine includes an intake-side hydraulic drivevariable valve timing mechanism configured to change a valve timing ofan intake valve by changing a rotation phase of an intake camshaftrelative to a crankshaft, an exhaust-side hydraulic drive variable valvetiming mechanism configured to change a valve timing of an exhaust valveby changing a rotation phase of an exhaust camshaft relative to thecrankshaft, and a lock mechanism configured to mechanically lock therelative rotation phase of the intake camshaft at an intermediate phasebetween a most retarded phase and a most advanced phase. The controldevice includes a controller. The controller controls the relativerotation phase of the exhaust camshaft in accordance with the relativerotation phase of the intake camshaft. When a request for locking therelative rotation phase of the intake camshaft at the intermediate phaseis generated, the controller controls the relative rotation phase of theexhaust camshaft such that the relative rotation phase of the exhaustcamshaft is changed to a phase corresponding to the intermediate phaseindependently from the relative rotation phase of the intake camshaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the configuration of a controldevice for an internal combustion engine according to one embodiment andan internal combustion engine as the control target of the controldevice;

FIG. 2 is a schematic diagram showing the configuration of anintake-side variable valve timing mechanism of the embodiment;

FIGS. 3A and 3B are cross-sectional views showing a lock mechanism ofthe embodiment;

FIGS. 4A and 4B are timing diagrams each representing an example ofchanges in relative rotation phases of an intake camshaft and an exhaustcamshaft in conventional control when a request for locking the relativerotation phase of the intake camshaft at an intermediate phase isgenerated;

FIG. 5 is a flowchart representing steps of a procedure for setting acontrol target of the relative rotation phase of the exhaust camshaft ofthe embodiment; and

FIGS. 6A and 6B are timing diagrams each representing an example ofchanges in the relative rotation phases of the intake camshaft and theexhaust camshaft in the embodiment when a request for locking therelative rotation phase of the intake camshaft at the intermediate phaseis generated.

MODES FOR CARRYING OUT THE INVENTION

A control device for an internal combustion engine according to oneembodiment of the present invention will now be described with referenceto FIGS. 1 to 6B. The control device is employed for an on-vehicleinternal combustion engine.

As shown in FIG. 1, an intake passage 11 and an exhaust passage 12 areconnected to each of the cylinders of an internal combustion engine 10.The engine 10 has an intake valve 14, which selectively permits andblocks communication between the intake passage 11 and a combustionchamber 13. The engine 10 also has an exhaust valve 15, whichselectively permits and blocks communication between the exhaust passage12 and the combustion chamber 13.

A piston is arranged in each cylinder in a reciprocally movable manner.A crankshaft 16 is joined to each of the pistons via a connecting rod.

An intake camshaft 17 and an exhaust camshaft 18 are also provided, toeach of which rotation of the crankshaft 16 is transmitted through anon-illustrated timing chain. The intake camshaft 17 and the exhaustcamshaft 18 rotate to selectively open and close the intake valve 14 andthe exhaust valve 15, respectively.

In the engine 10, the air drawn into the combustion chamber 13 via theintake passage 11 and the fuel injected from a non-illustrated fuelinjection valve are mixed with each other to form air-fuel mixture. Thepistons are reciprocated through combustion pressure, which is producedby burning the air-fuel mixture. The crankshaft 16 is thus rotatedthrough the pistons. Exhaust air, which is produced by burning theair-fuel mixture, is discharged via the exhaust passage 12.

The engine 10 has an intake-side variable valve timing mechanism 30,which changes the valve timing of the intake valve 14 by changing therotation phase of the intake camshaft 17 relative to the crankshaft 16(hereinafter, referred to simply as the relative rotation phase of theintake camshaft 17). The engine 10 also has an exhaust-side hydraulicdrive variable valve timing mechanism 60, which changes the valve timingof the exhaust valve 15 by changing the rotation phase of the exhaustcamshaft 18 relative to the crankshaft 16 (hereinafter, referred tosimply as the relative rotation phase of the exhaust camshaft 18).

The intake-side variable valve timing mechanism 30 will now bedescribed.

With reference to FIG. 2, the intake-side variable valve timingmechanism 30 includes a vane rotor 31 and a housing 33. The vane rotor31 is fixed to the intake camshaft 17 and rotates integrally with theintake camshaft 17. The housing 33 is arranged around the vane rotor 31.Rotation of the crankshaft 16 is transmitted to the housing 33 via thetiming chain.

The housing 33 and the vane rotor 31 are arranged coaxial with eachother. Four projections 34, which project toward the axis L1 of theintake camshaft 17, are formed on the inner circumferential surface ofthe housing 33 and spaced apart circumferentially at predeterminedintervals.

The vane rotor 31 has four vanes 32 on the outer circumferentialsurface. Each vane 32 is located between adjacent two of the projections34 of the housing 33. The space defined by end faces of each adjacentpair of the projections 34 of the housing 33, the inner circumferentialsurface of the housing 33, and the outer circumferential surface of thevane rotor 31 is thus divided into two hydraulic chambers (a phaseadvancing chamber 35 and a phase retarding chamber 36) by thecorresponding one of the vanes 32.

When oil is supplied to the phase advancing chambers 35 and drained fromthe phase retarding chambers 36 in the intake-side variable valve timingmechanism 30, the vane rotor 31 is rotated relative to the housing 33clockwise as viewed in FIG. 2 and the relative rotation phase of theintake camshaft 17 is advanced. That is, the relative rotation phase ofthe intake camshaft 17 is changed to the leading side in the rotatingdirection. This advances the valve timing of the intake valve 14.

If oil is supplied to the phase retarding chambers 36 and drained fromthe phase advancing chambers 35, the vane rotor 31 is rotated relativeto the housing 33 counterclockwise as viewed in FIG. 2 and the relativerotation phase of the intake camshaft 17 is retarded. The relativerotation phase of the intake camshaft 17 is changed to the trailing sidein the rotating direction. This retards the valve timing of the intakevalve 14.

The exhaust-side variable valve timing mechanism 60 is configuredbasically identical with the intake-side variable valve timing mechanism30. Repetitive description of the exhaust-side variable valve timingmechanism 60 is thus omitted herein.

The intake-side variable valve timing mechanism 30 has a lock mechanism40, which restricts relative rotation of the intake camshaft 17 when theengine 10 is started. The lock mechanism 40 is arranged only in theintake-side variable valve timing mechanism 30. The exhaust-sidevariable valve timing mechanism 60 has no lock mechanism.

The lock mechanism 40 will now be described.

As illustrated in FIGS. 2, 3A, and 3B, the lock mechanism 40 is providedin one of the vanes 32 of the vane rotor 31.

Referring to FIGS. 3A and 3B, the vane 32 having the lock mechanism 40has a stepped accommodation hole 41, which extends parallel to the axisL1 of the intake camshaft 17. A lock pin 42 is accommodated in theaccommodation hole 41 in a projectable and retractable manner.

The lock pin 42 has a pressure receiving portion 42 a, which is shapedto have an increased diameter, at the basal end. The lock pin 42 ismovable in the direction of the axis L1 of the intake camshaft 17 in astate in which the outer circumferential surface of the pressurereceiving portion 42 a is held in slidable contact with the innercircumferential surface of the accommodation hole 41. The lock pin 42 isurged by a coil spring 43 in such a direction that the distal end of thelock pin 42 exits to the exterior through a stepped portion 41 a of theaccommodation hole 41.

An unlocking pressure chamber 44, which is an annular space, is definedbetween the pressure receiving portion 42 a of the lock pin 42 and thestepped portion 41 a of the accommodation hole 41.

When oil is supplied to the unlocking pressure chamber 44 in the lockmechanism 40, the lock pin 42 is urged by the pressure produced by theoil and moves against the urging force of the coil spring 43 in thedirection in which the lock pin 42 is retracted into the accommodationhole 41. If the oil is drained from the unlocking pressure chamber 44,the lock pin 42 is moved by the urging force of the coil spring 43 inthe direction in which the lock pin 42 protrudes from the accommodationhole 41.

The housing 33 has a lock hole 45, which serves as a recess configuredto receive the distal end of the lock pin 42. The lock hole 45 isarranged at such a position that the relative rotation phase of theintake camshaft 17 corresponds to an intermediate position between themost retarded phase, which is the control limit phase in the phaseretarding direction in a controllable range, and the most advancedphase, which is the control limit phase in the phase advancingdirection. The intermediate phase is defined as a locked phase, which isthe relative rotation phase of the intake camshaft 17 that is suitablefor starting the engine 10.

As shown in FIGS. 2, 3A, and 3B, the housing 33 has a ratchet groove 46,which is shallower than the lock hole 45. The ratchet groove 46 extendsfrom the lock hole 45 to the phase retarding side along thecircumference of the housing 33.

When the relative rotation phase of the intake camshaft 17 is in therange corresponding to the location of the ratchet groove 46, the distalend of the lock pin 42 is inserted into the ratchet groove 46 bydraining oil from the unlocking pressure chamber 44. Then, when theintake camshaft 17 is relatively rotated to the intermediate positionthrough ratchet action, or, in other words, when the lock pin 42 ismoved to the position of the lock hole 45 in the housing 33 throughrelative rotation of the intake camshaft 17, the lock pin 42 is insertedinto the lock hole 45. This mechanically locks the vanes 32 of theintake-side variable valve timing mechanism 30 to the housing 33. As aresult, the relative rotation phase of the intake camshaft 17 is lockedat the intermediate phase.

If oil is supplied to the unlocking pressure chamber 44 in a lockedstate, in which the vanes 32 of the intake-side variable valve timingmechanism 30 are mechanically locked to the housing 33, the lock pin 42exits the lock hole 45 and the lock mechanism 40 is switched to anunlocked state.

As illustrated in FIG. 2, the engine 10 has an oil pump 20, whichsupplies oil to the intake-side variable valve timing mechanism 30 andthe lock mechanism 40. The intake-side variable valve timing mechanism30, the lock mechanism 40, and the oil pump 20 are connected together bya hydraulic circuit, which includes an oil control valve 50. Operationof the oil control valve 50 is controlled to control the supply-drainagemodes of oil to the phase advancing chambers 35 and the phase retardingchambers 36 of the intake-side variable valve timing mechanism 30 andthe unlocking pressure chamber 44 of the lock mechanism 40.

The oil control valve 50 is connected to the oil pan 21, which retainsoil, via a supply passage 51. The oil pump 20 is arranged in the supplypassage 51. The oil from the oil pump 20 is supplied to the oil controlvalve 50 via the supply passage 51. The oil control valve 50 is alsoconnected to an oil pan 21 via a drainage passage 52. Oil is drainedfrom the phase advancing chambers 35, the phase retarding chambers 36,or the lock mechanism 40 into the oil pan 21 via the drainage passage52.

The oil control valve 50 is connected to the phase advancing chambers 35and the phase retarding chambers 36 of the intake-side variable valvetiming mechanism 30 via a phase advancing oil line 53 and a phaseretarding oil line 54, respectively. The oil control valve 50 isconnected also to the unlocking pressure chamber 44 of the lockmechanism 40 via a lock oil line 55.

The engine 10 has a non-illustrated hydraulic circuit that connects theexhaust-side variable valve timing mechanism 60 and the oil pump 20 toeach other.

That is, with reference to FIG. 1, an oil control valve 70 is arrangedin the hydraulic circuit of the exhaust-side variable valve timingmechanism 60, and operation of the oil control valve 70 is controlled tocontrol supply-drainage modes of oil for a phase advancing chamber and aphase retarding chamber of the exhaust-side variable valve timingmechanism 60. The hydraulic circuit is configured basically identicalwith the hydraulic circuit of the intake-side variable valve timingmechanism 30. Therefore, repetitive description of the hydraulic circuitof the exhaust-side variable valve timing mechanism 60 is omittedherein.

As illustrated in FIG. 1, various sensors are employed to detect thetraveling state of the vehicle and the operating state of the engine 10.

The sensors include, for example, a vehicle speed sensor for detectingthe traveling speed of the vehicle, an accelerator sensor for detectingthe accelerator depression amount, a throttle sensor for detecting theopening degree of the throttle valve, an air flowmeter for detecting theintake air amount, and a temperature sensor for detecting the enginetemperature. The sensors also include sensors such as a crank anglesensor for detecting the engine speed, which is the rotation speed ofthe crankshaft 16, an intake-side cam angle sensor for detecting therelative rotation phase of the intake camshaft 17, which is the valvetiming of the intake valve 14, and an exhaust-side cam angle sensor fordetecting the relative rotation phase of the exhaust camshaft 18, whichis the valve timing of the exhaust valve 15.

Various types of control of the engine 10 are executed by an electroniccontrol unit 90, which includes a microcomputer, for example. Theelectronic control unit 90 receives detection signals from the varioussensors and carries out various calculations based on the detectionsignals. Based on the results of the calculations, the electroniccontrol unit 90 performs throttle control, which is control of theopening degree of the throttle valve, fuel injection control, andignition timing control in known modes. The electronic control unit 90includes a controller 91, which carries out operation control of thevariable valve timing mechanisms 30, 60 and the lock mechanism 40. Theelectronic control unit 90 configures a control device for an internalcombustion engine. The engine 10 and the electronic control unit 90configure a control system for an internal combustion engine.

The throttle control is executed in the manner described below. That is,a requested intake air amount, which is the control target of the intakeair amount, is calculated based on the accelerator depression amount andthe engine speed. Subsequently, based on the requested intake air amountand the engine speed, a target throttle opening degree, which is thecontrol target of the throttle opening degree, is calculated. Operationof a motor for selectively opening and closing the throttle valve iscontrolled such that the target throttle opening degree and the actualthrottle opening degree become equal to each other.

Operation control of the intake-side variable valve timing mechanism 30,which is operation control of the oil control valve 50, is performed inthe manner described below.

When the engine 10 is in operation, operation of the oil control valve50 is controlled basically to supply oil into the unlocking pressurechamber 44 of the lock mechanism 40. The lock mechanism 40 is thus heldin an unlocked state. Also, the control target of the relative rotationphase of the intake camshaft 17, which is the control target of thevalve timing of the intake valve 14, is calculated based on theaforementioned requested intake air amount and engine speed. Theoperation control of the oil control valve 50 is performed such that thecalculated control target and the actual relative rotation phase of theintake camshaft 17 become equal to each other. The operation control ofthe oil control valve 50 is carried out to achieve efficientintroduction of intake air into the combustion chamber 13 of the engine10.

Operation control of the exhaust-side variable valve timing mechanism60, which is operation control of the oil control valve 70, is executedin the manner described below.

The control target of the relative rotation phase of the exhaustcamshaft 18, which is the control target of the valve timing of theexhaust valve 15, is calculated using the control target of the relativerotation phase of the intake camshaft 17 and the control target of thevalve overlap amount, which is calculated based on the current enginestate in a known mode. Valve overlap refers to a period in which theintake valve 14 and the exhaust valve 15 are both open. The operationcontrol of the oil control valve 70 is carried out such that the controltarget of the relative rotation phase of the exhaust camshaft 18 and theactual relative rotation phase of the exhaust camshaft 18 become equalto each other.

In the present embodiment, engine operation in a combustion cycle withan expansion ratio exceeding the compression ratio (Atkinson cycle) iscarried out in a moderate-load moderate-speed range, in which therequested intake air amount and the engine speed are both moderate. Forexample, by controlling the valve timing of the intake valve 14 tobecome the most retarded timing, which is the most retarded timing inthe control range, the valve closing time of the intake valve 14 is setto a predetermined time in a compression stroke. In this manner, engineoperation in Atkinson cycle is brought about. Such engine operation inAtkinson cycle improves thermal efficiency compared to engine operationin a typical combustion cycle with a compression ratio equal to theexpansion ratio (Otto cycle). This improves the fuel efficiency.

In the process of stopping the engine 10, operation control of the oilcontrol valve 50 is executed such that the relative rotation phase ofthe intake camshaft 17 corresponds to the intermediate rotation phaseand that oil is drained from the unlocking pressure chamber 44. In thismanner, the relative rotation phase of the intake camshaft 17 is lockedat the intermediate phase by means of the lock mechanism 40.

Therefore, the relative rotation phase of the intake camshaft 17 ismaintained at the intermediate phase, which is suitable for enginestart, in the engine starting process. The engine 10 is thus startedappropriately.

In conventional operation control of the oil control valve 70, theproblem described below may occur.

That is, as represented in FIGS. 4A and 4B, at time t11 in the stoppingprocess of the engine 10, the relative rotation phase P_(in) of theintake camshaft 17 is at the first phase P1, which is advanced withrespect to the intermediate phase P_(rock). If, at this stage, a requestfor locking the relative rotation phase P_(in) of the intake camshaft 17at the intermediate phase P_(rock) is generated, the relative rotationphase P_(in) of the intake camshaft 17 is changed to fall within apredetermined phase range (P3≦P_(in)≦P2) corresponding to the locationof the ratchet groove 46. At time t12, at which the relative rotationphase P_(in) of the intake camshaft 17 falls within the aforementionedpredetermined phase range, oil is drained from the unlocking pressurechamber 44. The distal end of the lock pin 42 is thus inserted into theratchet groove 46 at time t13. At time t14, the relative rotation phaseP_(in) of the intake camshaft 17 is locked at the intermediate phaseP_(rock).

At this stage, in the conventional operation control of the oil controlvalve 70, the relative rotation phase Q_(ex) of the exhaust camshaft 18is controlled in accordance with the relative rotation phase P_(in) ofthe intake camshaft 17.

That is, referring to FIGS. 4A and 4B, at time t11, the relativerotation phase Q_(ex) of the exhaust camshaft 18 is the first phase Q1,which is advanced with respect to the phase Q_(rock) corresponding tothe intermediate phase P_(rock). The phase Q_(rock) is such a phasethat, as long as the relative rotation phase P_(in) of the intakecamshaft 17 is the intermediate phase P_(rock) and the relative rotationphase Q_(ex) of the exhaust camshaft 18 is the phase Q_(rock), the valveoverlap amount of the intake valve 14 and the exhaust valve 15 becomessuitable for the current engine operating state. The phase Q_(rock) isset in advance through experimentation the like.

In the period from time t11 to time t14, the relative rotation phaseQ_(ex) of the exhaust camshaft 18 is changed in a manner following therelative rotation phase P_(in) of the intake camshaft 17.

As has been described, the exhaust-side variable valve timing mechanism60 has no lock mechanism. Accordingly, if the relative rotation phaseP_(in) of the intake camshaft 17 is abruptly changed to the intermediatephase P_(rock) through relative rotation of the intake camshaft 17 inthe period from time t13 to time t14, the relative rotation phase P_(in)of the intake camshaft 17 is mechanically locked at the intermediatephase P_(rock) at time t14. However, since the exhaust camshaft 18 hasbeen relatively rotated abruptly in the phase advancing direction, therelative rotation phase Q_(ex) of the exhaust camshaft 18 overshoots thephase Q_(rock), which corresponds to the intermediate phase P_(rock).This rapidly changes the engine output and thus lowers the drivability.

In the present embodiment, to restrain the aforementioned disadvantage,the relative rotation phase Q_(ex) of the exhaust camshaft 18 iscontrolled by means of the electronic control unit 90 in the mannerdescribed below. That is, if a request for locking the relative rotationphase P_(in) of the intake camshaft 17 at the intermediate phaseP_(rock) is generated, the relative rotation phase Q_(ex) of the exhaustcamshaft 18 is controlled such that the relative rotation phase Q_(ex)of the exhaust camshaft 18 is changed to the phase Q_(rock), whichcorresponds to the intermediate phase P_(rock), independently from therelative rotation phase P_(in) of the intake camshaft 17. Morespecifically, the relative rotation phase Q_(ex) of the exhaust camshaft18 is controlled such that the relative rotation phase Q_(ex) of theexhaust camshaft 18 is changed directly to the phase Q_(rock), whichcorresponds to the intermediate phase P_(rock).

The request for locking the relative rotation phase P_(in) of the intakecamshaft 17 at the intermediate phase P_(rock) may be generated when theengine 10 is in the stopping process. It is thus preferable to controlthe relative rotation phase of the exhaust camshaft 18 independentlyfrom the relative rotation phase of the intake camshaft 17 when theengine 10 is in the stopping process.

Next, with reference to FIG. 5, steps of a procedure of setting thecontrol target Q_(extrg) of the relative rotation phase of the exhaustcamshaft 18 will be described. The series of procedure represented inFIG. 5 is executed by the controller 91 repeatedly at predeterminedintervals.

With reference to FIG. 5, in the procedure, a determination is made asto whether a request for locking the relative rotation phase P_(in) ofthe intake camshaft 17 at the intermediate phase P_(rock) has beengenerated (Step S1). That is, the controller 91 determines whether arequest for locking the relative rotation phase P_(in) of the intakecamshaft 17 at the intermediate phase P_(rock) has been generated.

If a negative determination is made in Step S1 (Step S1: NO), a valuedetermined by adding a predetermined value to the control targetP_(intrg) of the relative rotation phase of the intake camshaft 17 isset as the control target Q_(extrg) of the relative rotation phase ofthe exhaust camshaft 18 (Step S3). The procedure is then suspended. Theaforementioned predetermined value is varied in accordance with theengine operating state. The actual relative rotation phase of theexhaust camshaft 18 is controlled to become equal to the control targetQ_(extrg) of the relative rotation phase of the exhaust camshaft 18. Asa result, the valve overlap amount of the intake valve 14 and theexhaust valve 15 is set to a value suitable for the engine operatingstate.

In contrast, when a positive determination is made in Step S1 (Step S1:YES), the phase Q_(rock), which corresponds to the intermediate phaseP_(rock) is set as the control target Q_(extrg) of the relative rotationphase of the exhaust camshaft 18 (Step S2). The procedure is thensuspended. That is, when the controller 91 determines that a request forlocking the relative rotation phase P_(in) of the intake camshaft 17 atthe intermediate phase F_(rock) has been generated, the controller 91controls the relative rotation phase of the exhaust camshaft 18independently from the relative rotation phase of the intake camshaft17.

Operation of the present embodiment will now be described.

When the engine is in operation, the relative rotation phase Q_(ex) ofthe exhaust camshaft 18 is controlled basically in accordance with therelative rotation phase P_(in) of the intake camshaft 17. That is, thevalve timing of the exhaust valve 15 is controlled in accordance withthe valve timing of the intake valve 14 in a favorable manner. In otherwords, the valve timing of the exhaust valve 15 is controlled in amanner following the valve timing of the intake valve 14 in a favorablemanner.

As represented in FIGS. 6A and 6B, as a request for locking the relativerotation phase P_(in) of the intake camshaft 17 at the intermediatephase P_(rock) is generated at time t1, the relative rotation phaseQ_(ex) of the exhaust camshaft 18 is changed directly to the phaseQ_(rock), which corresponds to the intermediate phase P_(rock),independently from the relative rotation phase P_(in) of the intakecamshaft 17 (at time t2). That is, the controller 91 maintains therelative rotation phase Q_(ex) of the exhaust camshaft 18 at theconstant phase Q_(rock) regardless of the relative rotation phase P_(in)of the intake camshaft 17. As a result, the relative rotation phaseP_(in) of the intake camshaft 17 is locked at the intermediate phaseP_(rock) and the relative rotation phase Q_(ex) of the exhaust camshaft18 is maintained without overshooting the phase Q_(rock), which is setin accordance with the intermediate phase P_(rock). This restrains anabrupt change of engine output caused by locking the valve timing of theintake valve 14 at the valve timing corresponding to the intermediatephase P_(rock).

The control device for an internal combustion engine according to theabove described embodiment has the following advantages.

(1) The electronic control unit 90 controls the relative rotation phaseQ_(ex) of the exhaust camshaft 18 in accordance with the relativerotation phase P_(in) of the intake camshaft 17. The electronic controlunit 90 includes the controller 91. When a request for locking therelative rotation phase P_(in) of the intake camshaft 17 at theintermediate phase P_(rock) is generated, the controller 91 controls therelative rotation phase Q_(ex) of the exhaust camshaft 18 such that therelative rotation phase Q_(ex) of the exhaust camshaft 18 is changed tothe phase Q_(rock), which corresponds to the intermediate phaseP_(rock), independently from the relative rotation phase P_(in) of theintake camshaft 17. More specifically, when a request for locking therelative rotation phase P_(in) of the intake camshaft 17 at theintermediate phase P_(rock) is generated, the controller 91 controls therelative rotation phase P_(in) of the intake camshaft 17 such that therelative rotation phase P_(in) of the intake camshaft 17 is changed tofall within the predetermined phase range (P3≦P_(in)≦P2), whichcorresponds to the ratchet groove 46. At this time, the controller 91controls the relative rotation phase of the exhaust camshaft 18 suchthat the relative rotation phase Q_(ex) of the exhaust camshaft 18 ischanged to the phase Q_(rock), which corresponds to the intermediatephase P_(rock), independently from the relative rotation phase P_(in) ofthe intake camshaft 17.

In this configuration, the relative rotation phase Q_(ex) of the exhaustcamshaft 18 is controlled basically in accordance with the relativerotation phase P_(in) of the intake camshaft 17. The valve timing of theexhaust valve 15 is thus controlled in accordance with the valve timingof the intake valve 14 in a favorable manner. When a request for lockingthe relative rotation phase P_(in) of the intake camshaft 17 at theintermediate phase P_(rock) is generated, the relative rotation phaseP_(in) of the intake camshaft 17 is locked at the intermediate phaseP_(rock) and the relative rotation phase Q_(ex) of the exhaust camshaft18 is maintained without overshooting the phase Q_(rock), which is setin accordance with the intermediate phase. This restrains, in a desiredmanner, an abrupt change of engine output caused by locking the valvetiming of the intake valve 14 at the valve timing corresponding to theintermediate phase P_(rock).

The control device for an internal combustion engine according to thepresent invention is not limited to the configuration illustrated in theabove-described embodiment, but may be modified as follows.

The ratchet groove may extend from the lock hole to the phase advancingside.

1. A control device for an internal combustion engine, wherein theengine includes: an intake-side hydraulic drive variable valve timingmechanism configured to change a valve timing of an intake valve bychanging a rotation phase of an intake camshaft relative to acrankshaft; an exhaust-side hydraulic drive variable valve timingmechanism configured to change a valve timing of an exhaust valve bychanging a rotation phase of an exhaust camshaft relative to thecrankshaft; and a lock mechanism configured to mechanically lock therelative rotation phase of the intake camshaft at an intermediate phasebetween a most retarded phase and a most advanced phase, wherein thelock mechanism is provided only in the intake-side variable valve timingmechanism, the control device comprises a controller, when no requestfor locking the relative rotation phase of the intake camshaft at theintermediate phase is generated, the controller controls the relativerotation phase of the exhaust camshaft in accordance with the relativerotation phase of the intake camshaft, and when a request for lockingthe relative rotation phase of the intake camshaft at the intermediatephase is generated, the controller controls the relative rotation phaseof the exhaust camshaft such that the relative rotation phase of theexhaust camshaft is changed to a phase corresponding to the intermediatephase independently from the relative rotation phase of the intakecamshaft.
 2. The control device according to claim 1, wherein the lockmechanism includes a stopper member arranged in a first rotation bodythat rotates integrally with one of the crankshaft and the intakecamshaft, and a recess formed in a second rotation body that rotatesintegrally with the other one of the crankshaft and the intake camshaft,the recess being configured to receive the stopped member, the lockmechanism is configured to lock the relative rotation phase of theintake camshaft at the intermediate phase by inserting the stoppermember into the recess, a ratchet groove is arranged in the secondrotation body, wherein the ratchet groove extends from the recess to aphase advancing side or a phase retarding side and is shallower than therecess, the controller is configured to control the relative rotationphase of the intake camshaft in addition to the relative rotation phaseof the exhaust camshaft, when the request for locking the relativerotation phase of the intake camshaft at the intermediate phase isgenerated, the controller controls the relative rotation phase of theintake camshaft such that the relative rotation phase of the intakecamshaft is changed to fall within a predetermined phase rangecorresponding to the ratchet groove and controls the relative rotationphase of the exhaust camshaft such that the relative rotation phase ofthe exhaust camshaft is changed directly to the phase corresponding tothe intermediate phase.
 3. The control device according to claim 1,wherein the request for locking the relative rotation phase of theintake camshaft at the intermediate phase is generated when the engineis in a stopping process, and when the engine is in the stoppingprocess, the controller controls the relative rotation phase of theexhaust camshaft independently from the relative rotation phase of theintake camshaft.
 4. The control device according to claim 1, wherein thecontroller determines whether the request for locking the relativerotation phase of the intake camshaft at the intermediate phase has beengenerated, and when determining that the request has been generated, thecontroller controls the relative rotation phase of the exhaust camshaftindependently from the relative rotation phase of the intake camshaft.5. The control device according to claim 2, wherein the request forlocking the relative rotation phase of the intake camshaft at theintermediate phase is generated when the engine is in a stoppingprocess, and when the engine is in the stopping process, the controllercontrols the relative rotation phase of the exhaust camshaftindependently from the relative rotation phase of the intake camshaft.6. The control device according to claim 2, wherein the controllerdetermines whether the request for locking the relative rotation phaseof the intake camshaft at the intermediate phase has been generated, andwhen determining that the request has been generated, the controllercontrols the relative rotation phase of the exhaust camshaftindependently from the relative rotation phase of the intake camshaft.7. The control device according to claim 3, wherein the controllerdetermines whether the request for locking the relative rotation phaseof the intake camshaft at the intermediate phase has been generated, andwhen determining that the request has been generated, the controllercontrols the relative rotation phase of the exhaust camshaftindependently from the relative rotation phase of the intake camshaft.8. The control device according to claim 5, wherein the controllerdetermines whether the request for locking the relative rotation phaseof the intake camshaft at the intermediate phase has been generated, andwhen determining that the request has been generated, the controllercontrols the relative rotation phase of the exhaust camshaftindependently from the relative rotation phase of the intake camshaft.